Download this program
See how disgusting the wireless interference is and set your router to a less used channel. Ideally use channels 1, 6, or 11. Chances are options will be non existent because everyone and their dog is using wifi at your apartment. There are a few bad options to fix it. One would be switching to the 5ghz band which would be ideal except many wireless devices do not support it. Another would be to get a router that allows you to set the euro or japan bands and set the router to channel 13 (Illegal in the USA, but I really doubt the FCC will ever notice it.) Third would be to move out or line your walls with lead
If the device you are trying to get the wireless is not going to move much you can try getting some power line adapters and use those. The Time Warner here gave them out for free but a tech had to go out and install them or you can buy a set some what cheep at newegg.
Also the problem isn't limited to other wi-fi networks its anything that uses the 2.4ghz band. baby monitors, microwaves, wireless controllers ect